1. Field of the Invention
The present invention relates to an autoleveling device for a vehicle with a hydro-pneumatic suspension using hydro-pneumatic suspension units for suspending respective wheels.
2. Description of the Prior Art
Such a kind of suspension has been practically used for some vehicles because it is able to keep a vehicle height at a determined level even when a load acting upon the vehicle varies as due to variations in number of passengers. In such autoleveling devices for maintaining the vehicle height, there has been known a built-in type wherein an autoleveling device is built into each suspension unit which is provided between each suspension member and the vehicle body, and also an outlying type wherein an autoleveling device is arranged on a vehicle body at an intermediate location between right and left wheels so as to operate in response to vertical displacements (variations in vehicle height) of axle tubes or rotating movements of an antiroll bar connecting suspension members.
The outlying type autoleveling device makes possible the use of small and simple suspension units in comparison with the units required with the built-in type autoleveling device and has an advantage in that the device is not affected by rolling of the vehicle when turning because the device operates at the mid portion of the vehicle in response to averaged displacements of the suspension members for the right and left wheels. The present invention relates to an improvement of the outlying type autoleveling device.
In general, a conventional autoleveling device actuates oil supply and exhaust valves by control members in response to variations in vehicle height for suplying and exhausting the oil from the suspension units, thereby maintaining the vehicle height. The variations in vehicle height are detected by variations in distance between the suspension member and vehicle body (e.g. detecting rotative positions of the antiroll bar). The and the distance between the suspension member and vehicle body varies greatly not only in response to load, but also in response to wheel hop (i.e. rapid up and down wheel movement) caused by uneveness of the roads. Because operative movements of the control members in response to the variations in the distance sometimes become quite large, they can require the size of a conventional autoleveling device to become too large to be put to practical use. Consequently, springs acting upon ends of the control members are generally used to balancingly support the control members. When the variation in the distance occurs, one of the springs is subjected at its end to the displacement so as to cause a variation in the balancing support of the control members, thereby enabling the control members to be proportionally responsive to the variations in the distance to limit the operative movements to a controllable range.
In such conventional devices, however, as the displacement of the suspension member is transmitted in a proportionally reduced amount to the control member, the operative movement of the control member is much smaller relative to the displacement of the suspension member, so that the displacement of the control member is prone to error resulting in incorrect autoleveling function.
Moreover, as the control members respond linearly to the variation in vehicle height, it is impossible to increase the displacement of the control members corresponding to the variation in vehicle height in the proximity of the standard height in order to improve the responsiveness of the control members to obtain the precise autoleveling function. In other words, if the displacement of the control members is increased, the operative movements of the control members become larger as a whole which would exceed the controllable range and make the autoleveling device too long to be put to practical use.